Tomio Ariyasu

Unidirectionality of an optically pumped far infrared ring laser

Abstract An experimental and theoretical investigation has been made on the unidirectional operation of an optically pumped far infrared ring laser. A ring laser operating on the 119 μm line of CH3OH experiences reversal of output direction in either case of (a) the pump frequency being tuned across the line center of the infrared pump transition or (b) the fir cavity being tuned across the far infrared line center. A model based on two-mode laser theory predicts the output directionality of the optically pumped fir ring laser.

Local Structure of ECR Process Plasma

Characteristics of an ECR process plasma produced by 2.45 GHz microwave radiation in hydrogen gas were studied, paying attention to the localized feature of ECR phenomenon in a nonuniform magnetic field. At a pressure of over 3 × 10-1 Pa, a strongly nonuniform axial temperature distribution of electrons was observed, and the temperature control was found to be possible mainly near the resonance region. It was verified that variation of the radial wall dimension of the vacuum chamber gave a remarkable influence to the plasma parameter near the resonance region. Spatial structure of the plasma in mirror and divergent magnetic field configurations was found to be nearly the same in a high-pressure-range over 1 × 10-1 Pa.

Influence of Local Feature of Electron Cyclotron Resonance Plasma on the Formation of Amorphous Hydrogenated Silicon Films

Amorphous hydrogenated silicon (a-Si:H) film synthesis in an electron cyclotron resonance (ECR) plasma in silane and/or hydrogen diluted gases is studied in correlation with the local feature of the plasma. Experiments are carried out in a divergent magnetic field configuration at a gas pressure of 4 Pa, and the microwave power input is varied up to 500 W. The highest deposition rate is obtained just near the resonance point and the optical gap of the film has the lowest value at this position. The photoconductivity of the films is found to be strongly dependent on the axial distance L between the substrate and the resonance point. The optimum position for the formation of high-quality a-Si:H films is found in the axial direction, and it varies with input microwave power. The distance L which gives the maximum photoconductivity is shifted with input microwave power. For instance, at a microwave power Pµ of about 50 W the highest photoconductivity is obtained at L=6 cm, while at Pµ=100 W, the highest value is obtained at L=8 cm. This feature is attributed to the local behavior of the plasma production and decomposition of radical species near the resonance zone.

Anisotropic unidirectional operation of an optically-pumped CH3OH ring laser

Abstract We report directional anisotropy of the outputs of an optically pumped far-infrared ring laser, which operates on the 119 μm line of CH3OH, with special emphasis on the effect of the Raman-type two-photon process on the unidirectional operation. By use of a Doppler broadened three-level system which allows the coexistence of two counterpropagating far infrared (fir) fields as well as a pump field in the cavity, an expression for the fir intensity determining equations is derived. A numerical calculation has been carried out to map the threshold contours on the parameter plane spanned by the cavity and pump detuning frequencies. The output directionality is shown to be a direct consequence of the gain anisotropy due to the two-photon process. Furthermore, it is also noted how the dynamic Stark effect modifies the threshold contours of the forward output.

Field-ion microscopy of the si(001) surface

Abstract The image formation and atomic structure of the Si(001) plane are examined using a field-ion microscope (FIM). The surface structure of this plane observed through the FIM showed several parallel bright lines in spite of forming the bulk lattice structure. This feature of the ion images is explained by the concept of dangling orbitals of surface Si atoms. Furthermore, at a higher electric field, the atoms of this plane had a rearranged (2 × 1) superstructure which is different from the bulk lattice plane. The FIM images obtained without thermal treatment revealed a dimer type or a zig-zag-chain type reconstruction and were inconsistent with a vacancy model. The atoms of the second layer underlying the superstructure were moved from the bulk sites to other sites along with the reconstruction of the topmost layer.

Measurement of temperature distribution and cooling speed in metal on IR radiation

Abstract Measurements were made on the temperature distribution and cooling rate of metal, on irradiation from a low pressure thermal plasma, with the surface radiance in the range of IR radiation. From the measured values the three-dimensional distribution of temperature in the metal was calculated by application of the theory of thermal conduction. We also measured these quantities on irradiation from a continuous-wave yttrium aluminium garnet laser and could explain the relation between the surface temperature and the hardness of irradiated metal. Moreover, the method was applied to determine the cooling rate for the production of amorphous ribbon by a single roller, and an interesting relation between the cooling rate and the crystal structure of the alloy was found.